1. Field of the Invention
The present invention relates to a multi-layer ceramic capacitor, more particularly, in which capacitance reliability is enhanced and defects such as electrical short and cracks are reduced.
2. Description of the Related Art
Of late, a smaller trend of electronic devices has led to a need for an ultra-capacity multi-layer ceramic capacitor. To this end, the multilayer ceramic capacitor is required to possess higher capacitance without increase in size. This necessitates a thinner ceramic layer, a thinner cover layer and a thinner internal electrode layer.
FIG. 1 is a side cross-sectional view illustrating an example of a conventional multi-layer ceramic capacitor.
Referring to FIG. 1, the multi-layer ceramic capacitor 10 includes cover layers provided on upper and lower surfaces thereof as outermost layers and a ceramic sintered body 11 having a plurality of ceramic layers disposed between the cover layers.
First and second internal electrodes 12a and 12b are arranged alternately between a corresponding one of the ceramic layers. First and second external electrodes 15a and 15b are formed on opposing sides of the ceramic sintered body 11 and connected to the first and second internal electrode 12a and 12b, respectively.
In this structure, to enhance capacitance of a capacitor without increase in size, the ceramic cover layers and internal electrodes 12a and 12b located at outermost portions need to be thinned. But this does not assure stable electrical properties of the internal electrodes 12a and 12b. Therefore, in order to allow for stable electrical properties of the internal electrodes while suppressing oxidization thereof, sintering should be performed at a reducing atmosphere where an oxygen partial pressure is regulated.
Sintering, when performed at such a reducing atmosphere having the oxygen partial pressure regulated, beneficially affects high-temperature reliability such as 150° C. IR characteristics. However, the outermost internal electrodes adjacent to the relatively thinner cover layers are observed to have been oxidized.
FIGS. 2A and 2B show electron probe micro analysis (EPMA) results analyzing mode of oxidization of the internal electrodes, which is caused by sintering at a reducing atmosphere having an oxygen partial pressure regulated, in manufacturing the conventional multi-layer ceramic capacitor.
With reference to the EPMA results of FIGS. 2A and 2B, oxide layers (indicated with “A” and “B”) formed of an Mg—Ni—O phase are observed to have been formed on areas adjacent to the outermost portions of the internal electrodes containing e.g., Ni.
As described above, these oxide layers are formed by performing sintering at a reducing atmosphere where the oxygen partial pressure is regulated. The oxide layers trigger structural defects such as cracks in cover portions, i.e., cover cracks and deteriorates electrical properties. This as a result undermines reliability and yield of the multi-layer ceramic capacitor.